This is a much bigger hurdle than it might seem; at any rate the biggest one for me personally. I have absolutely no idea how to create an exercise plan for myself, which exercises should I do and in which combination. And additionally, even if I had such a plan, I have no idea how to measure my progress, or whether and how to modify the plan depending on the progress.
Poor form is sometimes caused by fatigue, but that's about knowing your limitations.
Parent's point stands. Anything - in a reasonable sense - is better than nothing. If you do handstand push-ups day one, you deserve what you get.
After a few months you'll exhaust that (perhaps just take it out of the library?), and need more intermediate-level information:
Otherwise, some others have suggested a few Reddit threads; see also /r/fitness.
Don't over complicate things. Do 5 sets of 5 reps of:
* Bench Press (barbell)
* Front Squat (barbell)
* Dead Lift (barbell)
* Pull Ups (weight hangs off a chain linked through a squat belt)
Have 1.5 to 2 minutes of recovery between each set. Do this 2 to 3 times a week with as much weight as you can lift.
How to progress: Write down exactly what you lift in a notebook and attempt to do exactly what you lifted for the previous workout with the only change being an increase of 1 to 5 lbs on one of the sets.
Cost: A monthly gym membership or about 50 cents a pound for second hand weights. About $25 for a second hand barbell. $25 for a second hand bench w/rack. So starting out pickup 300lbs of weight which is about $150 plus the cost of the barbell, bench w/rack, and squat belt should set you back about ~$200 (or the cost of a gym membership for 4 months.).
Quiting social networks and watching/listening to news has helped to find time to learn and think about training.